The present invention relates generally to extracorporeal blood treatment. More particularly the invention relates to a blood treatment apparatus according to the preamble of claim 1 and a method according to the preamble of claim 8.
A conventional blood treatment apparatus, for instance a hemodialysis system or a hemodiafiltration system, contains a dialysis fluid circuit and a blood circuit. Each circuit is normally associated with at least one pump for transporting the fluid in question. Traditionally, peristaltic pumps have been used, and here the rotational speed of the pump can serve as a basis for determining the flow through the pump, e.g. in the blood circuit. For reasons of patient security and cost efficiency it is further advantageous to avoid including dedicated flow meters in the blood circuit. Hence, in designs including non-peristaltic blood pumps, it may be complicated to measure the blood flow accurately. In fact, also when peristaltic blood pumps are used, the blood flow measure derived from the pump speed may be unreliable. For example if the inlet pressure to the pump becomes negative (or more precisely inlet suction occurs), the rotational speed is a poor fluid flow indicator.
Hence, it is desirable to enable apparatus designs using other types of blood pumps than those operating according to a peristaltic principle. However, there is yet no such solution which renders an accurate blood flow measurement possible, and at the same time avoids the obvious infection/contamination risks associated with a multiple-use flow meter in the blood circuit. Of course, for cost reasons, any single-use flow meters cannot be of high-quality type.